1. Field of the Invention
The present invention generally relates to a voltage generating apparatus, and more particularly, to a voltage generating apparatus used for a headphone.
2. Description of Related Art
Along with the consumer electronic products get popularized, the function and the quality of being delicate of the peripheral commodities used in the consumer electronic products have enhanced. Taking a headphone suitable for listening music, all of the shape, function and quality thereof have been largely promoted. Driven by green energy consciousness, even a novel kind of power-saved headphone has been lunched already.
FIG. 1 is a diagram of a conventional voltage generating apparatus 100 for a headphone. The voltage generating apparatus 100 for a headphone needs to output two audio signals with different voltage ranges (for example, a left audio channel signal and a right audio channel signal), so that two operating amplifiers OP1 and OP2 are employed to respectively amplify the corresponding different input signals IL and IR. In the conventional voltage generating apparatus 100, both the operating amplifiers OP1 and OP2 need to receive two operating voltages VDD and VSS as the operating voltages thereof, wherein the operating voltage VSS is generated by a voltage generator 110 according to the operating voltage VDD and a grounding voltage GND (for example, VSS=GND−VDD). Usually, the voltage generator 110 is a charge pump circuit or a power converter composed of inductors and a switch, wherein the conventional voltage generating apparatus 100 always generates a fixed operating voltage VSS regardless of what implementation of the voltage generator 110.
Based on the above-mentioned situation, another conventional voltage generating apparatus 200 for a headphone was provided, as shown by FIG. 2. Referring to FIG. 2, the operating amplifier OP1 in the voltage generating apparatus 200 receives two operating voltages VDD and VSS respectively from a power supply 210 and a charge pump circuit 230, wherein the operating voltage VSS is generated by the charge pump circuit 230 according to an operating voltage VCC generated by another power supply 220. Therefore, a controller 240 in the voltage generating apparatus 200 can send a control signal CTRL to adjust the voltage VCC generated by the power supply 220 to further adjust the operating voltage VSS. However, the control signal CTRL generated by the controller 240 is a fixed value defined by a user or a designer, which can not be dynamically adjusted in response to the changed environment or changed demand.